this would be a free to use, domain name watcher.

the idea is that if someone wants to watch a domain for expiration, they enter the details here and a cron job is run against whois for the expiry. Then for each and every day after expiry until either the domain is reregistered (at which time a new expiry will be recorded) or becomes available for purchase.

In either case, the original requester is appraised once the domain is coming up for renewal/expiry and notified of any status changes.